Until recently there has persisted a fundamental dichotomy between two main types of telecommunication networks. The first type of telecommunication network, the telephone network, switches and transports predominantly voice, facsimile, and modulation-demodulation system (modem) traffic. The public switched telephone network (PSTN) is an example of this type of network. Telephone networks are also deployed privately within organizations such as corporations, banks, campuses, and government offices. The second type of telecommunication network, the data network, switches or routes and transports data and video between computers. The Internet is an example of a public data network; data networks may be privately deployed.
Telephone networks were developed and deployed earlier, followed by data networks. Telephone network infrastructures are ubiquitous, however, and as a result data networks typically are built, to a limited extent, using some components of telephone networks. For example, the end user access link to a data network in some cases is implemented with a dial-up telephone line. The dial-up telephone line thus connects the end user computer equipment to the data network access gateway. Also, high speed digital trunks interconnecting remote switches and routers of a data network are often leased from telephone long-haul carriers.
Nonetheless, telephone and data network infrastructures were typically deployed together with limited sharing of resources, especially with regards to the core components of the networks—the switches and routers that steer the payloads throughout the networks. Furthermore, multiservice network switches are used to provide a data path, or interface, between multiple networks, each of which may operate using a different type of data or according to a different networking standard protocol. Examples of the networking protocols supported by these multiservice switches include, but are not limited to, frame relay, voice, circuit emulation, T1 channelized, E1 channelized, and Asynchronous Transfer Mode (ATM). The cost of this redundancy coupled with advances in data network technology has led, where possible, to integrated network traffic comprising voice, data, facsimile, and modem information over a unified data network. As such, a network should now be able to accept, service, integrate, and deliver multiple types of data over its access links on a random, dynamic basis using a minimum set of hardware on a single platform. This is typically accomplished using network routers, or concentrators, that provide for dynamic allocation of network resources among the received channels of information on an as-needed basis, wherein the cost, size, and complexity of the router is reduced by minimizing the duplication of resources among router channels.
Typically, voice over data networks comprise the application of voice digitization and compression schemes to enable voice to be transported on networks originally developed to transport data. In providing integrated network traffic comprising voice information, voice over data networks represent a development intended to satisfy the necessity to integrate the transportation of voice and data in a cost-effective manner through equipment whose installation and operation limits potential disruption to ongoing organizational activities. Consequently, reliability is a major concern for organizations implementing voice over data networks.
Voice calls over packet networks are typically defined as either switched calls or permanent calls. In a switched call, the user enters a telephone number to select a call destination. In a permanent call, the end destination is fixed. Permanent calls are typically used to provide tie-line emulation for a connection between two telephone switches, for example, tie-line connections between central office facilities and branch or remote office facilities. Reliability of permanent tie-lines is of major concern because the tie-line is often relied on to provide instantaneous access between corporate facilities. As such, a failure of the equipment comprising a voice over data network may isolate corporate facilities. Therefore, there is a desire, when implementing permanent voice calls for tie-line replacements using voice over packet networks, to provide fault tolerance such that from the perspective of the external telephone equipment, the permanent voice connections provided are really permanent and reliable.
Two network types that are typically used to provide voice calls over packet networks are Internet Protocol (IP) and Frame Relay networks. Both IP and Frame Relay networks represent packet-shared networks for which bandwidth is consumed only when transmission occurs. The Frame Relay Forum has developed an Implementation Agreement, FRF.11, that defines the methods for providing voice over Frame Relay networks. While the FRF.11 protocol specification covers the formatting and transmission of packets over Frame Relay networks, it fails to deal with network configuration issues related to setting up and tearing down permanent connections, forwarding voice packets between FRF.11 call segments, and providing for multiple network routes or destinations. Consequently, there is a desire, relating to the reliability of permanent voice calls, to provide reliable permanent voice calls using FRF.11 voice links without modification of the FRF.11 format packets.